Our main goal is to develop new radioligands to be used for neuroimaging and the clinical routine patient studies by SPECT. We are involved in a collaborative effort with NIDDK in Bethesda with three different laboratories: Dr. Kenner Rice, Dr. Phil Skolnick, and Dr. Kenneth A. Jacobson to develop ligands for neuroimaging by SPECT. During this period two new ligands with high affinity and selectivity for the A-3 adenosine receptors and the diazepam-insensitive (DI) ligand for diazepam-insensitive receptors were developed respectively. The radioiodination methods with high radiolabelling yield were developed for these ligands. The radiochemical yield for these ligands was> 70% for 5 minutes at room temperature. Autoradiography, animal biodistribution, and SPECT imaging were performed for the DI ligands. This ligand is almost exclusively localized to the cerebellum in CNS and has linked to antagonize biochemical and behavioral effects of ethanol. 123I-sigma ligands were prepared for binding assays, tissue culture studies, and SPECT imaging in primates in order to further the understanding of the ligands. A patent entitled "Stannylated 3-Quinuclidinyl Benzilates and Methods of Preparing *AQNB" was filed in April, 1994 to the patent office. This 123IQNB can be applied to the clinical studies for patients to study the muscarinic receptors density in CNS. 123IQNB and 123IBZM ligands were prepared to study the muscarinic receptors and D-2 receptors for patients routinely by SPECT.